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At least two unknown planets could exist in our solar system beyond Pluto. / Credit: NASA/JPL-Caltech.

Astronomers are Predicting at Least Two More Large Planets in the Solar System

Article Updated: 23 Dec , 2015
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Could there be another Pluto-like object out in the far reaches of the Solar System? How about two or more?

Earlier this week, we discussed a recent paper from planet-hunter Mike Brown, who said that while there aren’t likely to be any bright, easy-to-find objects, there could be dark ones “lurking far away.” Now, a group of astronomers from the UK and Spain maintain at least two planets must exist beyond Neptune and Pluto in order to explain the orbital behavior of objects that are even farther out, called extreme trans-Neptunian objects (ETNO).

The presently known largest small bodies in the Kuiper Belt are likely not to be surpassed by any future discoveries. This is the conclusion of Dr. Michael Brown, et al. (Illustration Credit: Larry McNish, Data: M.Brown)

The presently known largest small bodies in the Kuiper Belt are likely not to be surpassed by any future discoveries. This is the conclusion of Dr. Michael Brown, et al. (Illustration Credit: Larry McNish, Data: M.Brown)

We do know that Pluto shares its region Solar System with more than 1500 other tiny, icy worlds along with likely countless smaller and darker ones that have not yet been detected.

In two new paper published this week, scientists at the Complutense University of Madrid and the University of Cambridge noted that the most accepted theory of trans-Neptunian objects is that they should orbit at a distance of about 150 AU, be in an orbital plane – or inclination – similar to the planets in our Solar System, and they should be randomly distributed.

But that differs from what is actually observed. What astronomers see are groupings of objects with widely disperse distances (between 150 AU and 525 AU) and orbital inclinations that vary between 0 to 20 degrees.

“This excess of objects with unexpected orbital parameters makes us believe that some invisible forces are altering the distribution of the orbital elements of the ETNO,” said Carlos de la Fuente Marcos, scientist at UCM and co-author of the study, “ and we consider that the most probable explanation is that other unknown planets exist beyond Neptune and Pluto.”

He added that the exact number is uncertain, but given the limited data that is available, their calculations suggest “there are at least two planets, and probably more, within the confines of our solar system.”

In their studies, the team analyzed the effects of what is called the ‘Kozai mechanism,’ which is related to the gravitational perturbation that a large body exerts on the orbit of another much smaller and further away object. They looked at how the highly eccentric comet 96P/Machholz1 is influenced by Jupiter (it will come near the orbit of Mercury in 2017, but it travels as much as 6 AU at aphelion) and it may “provide the key to explain the puzzling clustering of orbits around argument of perihelion close to 0° recently found for the population of ETNOs,” the team wrote in one of their papers.

The discovery images of 2012 VP113. Each one was taken about two hours apart on Nov. 5, 2012. Behind the object, you can see background stars and galaxies that remained still (from Earth's perspective) in the picture frame. Credit: Scott S. Sheppard: Carnegie Institution for Science

The discovery images of 2012 VP113. Each one was taken about two hours apart on Nov. 5, 2012. Behind the object, you can see background stars and galaxies that remained still (from Earth’s perspective) in the picture frame. Credit: Scott S. Sheppard: Carnegie Institution for Science

They also looked at the dwarf planet discovered last year called 2012 VP113 in the Oort cloud (its closest approach to the Sun is about 80 astronomical units) and how some researchers say it appears its orbit might be influenced by the possible presence of a dark and icy super-Earth, up to ten times larger than our planet.

“This Sedna-like object has the most distant perihelion of any known minor planet and the value of its argument of perihelion is close to 0°,” the team writes in their second paper. “This property appears to be shared by almost all known asteroids with semimajor axis greater than 150 au and perihelion greater than 30 au (the extreme trans-Neptunian objects or ETNOs), and this fact has been interpreted as evidence for the existence of a super-Earth at 250 au. In this scenario, a population of stable asteroids may be shepherded by a distant, undiscovered planet larger than the Earth that keeps the value of their argument of perihelion librating around 0° as a result of the Kozai mechanism.”

Of course, the theory put forth in two papers published by the team goes against the predictions of current models on the formation of the Solar System, which state that there are no other planets moving in circular orbits beyond Neptune.

But the team pointed to the recent discovery of a planet-forming disk around the star HL Tauri that lies more than 100 astronomical units from the star. HL Tauri is more massive and younger than our Sun and the discovery suggests that planets can form several hundred astronomical units away from the center of the system.

The team based their analysis by studying 13 different objects, so what is needed is more observations of the outer regions of our Solar System to determine what might be hiding out there.

Further reading:
Carlos de la Fuente Marcos, Raúl de la Fuente Marcos, Sverre J. Aarseth. “Flipping minor bodies: what comet 96P/Machholz 1 can tell us about the orbital evolution of extreme trans-Neptunian objects and the production of near-Earth objects on retrograde orbits”. Monthly Notices of the Royal Astronomical Society 446(2):1867-1873, 2015.

C. de la Fuente Marcos, R. de la Fuente Marcos. “Extreme trans-Neptunian objects and the Kozai mechanism: signalling the presence of trans-Plutonian planets? Monthly Notices of the Royal Astronomical Society Letters 443(1): L59-L63, 2014.

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13 Responses

  1. Snowball Solar System says:

    An alternative explanation is that of a former binary brown-dwarf Companion to the Sun, and Sun-Companion orbited around their gravitational balance point known as the former solar-system barycenter (SSB). The the centrifugal force of the Sun orbiting the SSB aligned the aphelia of plantesimals (in the opposite direction of the Companion), and those in the longest orbits (of the extended scattered disk) are still in relative alignment after the asymmetrical spiral-in merger of binary-Companion which gave it escape velocity from the Sun at 542 Ma, ushering in the Phanerozoic Eon and seeding the solar system with brown-dwarf lifeforms in the event known as the Cambrian Explosion.

    Stellar core collapse caused the components of binary-Companion to spiral in as its Sun-Companion wide-binary separation spiraled out at an exponential rate over time. The impingement of the solar system barycenter on Kuiper belt planetesimals perturbed some into the inner solar system, causing a bimodal late heavy bombardment as the SSB crossed the orbits of the Plutinos at 4,220 Ma and the peak concentration of the cubewanos at 3,900 Ma.

    • gopher65 says:

      There is no brown dwarf companion of the sun. This was ruled out by the WISE observations. No red dwarf either.

      • Snowball Solar System says:

        A former binary brown-dwarf Companion that received an escape-velocity kick in its asymmetrical spiral-in merger at 542 Ma, which I suggest coated the Kuiper belt objects with a volatilely-depleted (iron-wustite redox buffer) secondary debris-disk coating which thermally differentiates to form ‘TNO-crust’ meteorwrongs, many containing metallic-iron inclusions.

        The material dispersed in a binary spiral-in merger of a binary brown dwarf pair with differentiated metallic-iron cores will be siderophile depleted (depleted in nickel and platinum-group elements), which is why the material is dismissed as probable industrial slag despite sometimes having fusion crust with flow lines.

        https://hillscloud.wordpress.com/trans-neptunian-object-crust-tno-crust-meteorwrongs-2/

    • “…ushering in the Phanerozoic Eon and seeding the solar system with brown-dwarf lifeforms in the event known as the Cambrian Explosion” ………Can I buy some pot from you?

      • Snowball Solar System says:

        I have a bright-line cause for a bright-line event, while academia attempts to dismiss its confounding suddenness.

  2. mewo says:

    What is the likelihood that an Earth-sized planet would have escaped detection at ~250AU? I suspect it’s pretty high, actually.

  3. Greg says:

    The evidence is building towards at least two large planets beyond Neptune. Here is a reference to an even more interesting article from this website:

    http://www.newscientist.com/article/dn25711-two-giant-planets-may-cruise-unseen-beyond-pluto.html#.VLjDNbAo4dV

    A Jupiter sized object was already ruled out by Wise up to 10k AU as it would have been detectable. Neptune and Earth sized objects can still lurk anywhere out there. Solar system formation models are guesses at best and have been proven wrong and re-written many times as we learn about a huge diversity of planetary systems out there.
    As we have recently learned a planet more than 6 Earth masses is nearly always going to be a Neptune analog aka Ice Giant and not a super-Earth.
    Exciting times in astronomy, as it look like we have at least 10 planets now and probably a number more much farther out in the oort cloud that were captured from smaller stars in the Nebula that the Sun formed in. Now we just need sensitive enough instruments to spot them.

  4. resenmut says:

    I had the idea that there are two heavy objects outdoor behind Kuipert Belt cca 12 years ago. Mr. Robert Harrington had neary the same idea more than 20 years ago. He found it from analyse of Pioneers and Voyagers paths,.. I had nearly the same conclusions after analyse of pre-ancient astronomical depictions (Senmut astronom. map, Dendera Zodiac, funneral banner of markisa Tai, orient. carpet patterns,..),… Mike Brown with Chad Trujillo,..Mr. Rabinowitz,..found in for those objects forecasted positions of heavy object,..objects their first realy big planetoid Sedna,..on high eccetric eliptical orbit. Was it only coincidence? Realy not. Also other lately discovered planetoids which are on more eccentric orbits have their main axes,..orientation circa in one direction,..that direction what I also proposed,.. http://calgary.rasc.ca/images/Planets_and_Dwarfs_01_1000AU.png So what ancient sources speak to us? There are two heavy object behind Kuiper belt. One is on with cca 26000 years periodic orbit with aphelion in aprox. 1000AU, the second one is on very eccentric orbit with aphelion in aprox. 300AU. http://senmut.webs.com/ http://senmut.webs.com/nibiruancientcarpetsgot.htm. There are also some gaps in Kuiper Belt, sharp edges of Kuiper Belt, Titus-Bode Law,…what support this idea,.. Pavel

    • resenmut says:

      I had the idea that there are two heavy objects outdoor behind Kuipert Belt cca 12 years ago. Mr. Robert Harrington had neary the same idea more than 20 years ago. He found it from analyse of Pioneers and Voyagers paths,.. I had nearly the same conclusions after analyse of pre-ancient astronomical depictions (Senmut astronom. map, Dendera Zodiac, funneral banner of markisa Tai, orient. carpet patterns,..),… Mike Brown with Chad Trujillo,..Mr. Rabinowitz,..found in for those objects forecasted positions of heavy object,..objects their first realy big planetoid Sedna,..on high eccetric eliptical orbit. Was it only coincidence? Realy not. Also other lately discovered planetoids which are on more eccentric orbits have their main axes,..orientation circa in one direction,..that direction what I also proposed,.. calgary.rasc.ca/images/Planets_and_Dwarfs_01_1000AU.png So, what ancient sources speak to us? There are two heavy object behind Kuiper belt. One is on with cca 26000 years periodic orbit with aphelion in aprox. 1000AU, the second one is on very eccentric orbit with aphelion in aprox. 300AU. senmut.webs.com senmut.webs.com/nibiruancientcarpetsgot.htm. There are also some gaps in Kuiper Belt, sharp edges of Kuiper Belt, Titus-Bode Law,…what support this idea,..

  5. resenmut says:

    Sedna, Eris, Makemake, Haumea,..were discowered due to the fact that some astronomers have enough endavour, courage to search (with telescope, or theoretically) for big,..objects behind Pluto. We were persecuted, dehonested, casted out from work because to search for hidden objects behin Pluto (in our Solar System) was forebiden, highly not recommended by official authorities in Astronomy (till cca 2003!!! when Sedna was discovered). It was officialy said, that there is nothing heavyer behind Pluto. Who refused this conclusion was handled nearly like Giordano Bruno or Galileo Galilei in 17th,…century. So, I want to prewent similar situation due the conclusions from WISE survay. Hiden objects could be dark (albedo) and densty and so very heavy but invisible for WISE till now.

    • Greg says:

      I know what you mean. The atmosphere back in those days reminded me of what Christopher Columbus must have felt like. The solar system formation model dogma back then was almost as bad as a religion. You would be considered daft if you dared to argue against it. The irony is that science is supposed to be about eliminating bias and thinking outside the box in order to advance the field. The reality of the matter then was that solar system models were just crude guesses at best, but they were defended like sacred religious shrines. Of course there was scant evidence to argue for or against it. We only had one aged solar system to look at for ideas.
      I began speaking out when we were getting infrared data in on newly forming planetary systems. Sun-like stars had planets forming hundreds of AUs out, some of them gas giant size. The dogma then was that the space after the Kuiper belt was the end of the solar system, so to speak, much akin to how scholars in Columbus’ day thought that Eurasia-Africa was the end of the world. For goodness sake, the IAU’s definition for a planet is that it clears out it’s orbital space! Why couldn’t it be a large planet that cleared out this space? I read one article about how a nearby passing star may have cleared this space, which made no real sense, but the point is that anything but another planet was invoked to explain this empty space.
      Now that we are finding families of objects with commonly altered orbits out there, I believe that it is now proven beyond reasonable doubt that there are a few more real planets as the IAU defines them and not just dwarf planets waiting to be found. The problem still is that we don’t have sensitive enough instruments to find them, I believe mostly in part that nobody dared to believe that they could be there. I am sure someone is working on putting and end to this ignorance.
      As Socrates said, “Ignorance is the ultimate evil.” This ignorance is born out of preconceived biases and defended out of narrow egocentrism. It is shame to see it manifest so often in scientific fields, where the elimination of biases is considered the most essential principle. If an alien race were to evaluate us, I would believe they would still consider us to be unenlightened barbarians in possession of dangerous technology.

      • Snowball Solar System says:

        I can’t speak to the past, but I feel like I can hardly catch my breath today for the stifling presence of the Nice Model and Grand Tact.

        I’ve looked at enough sectioned images of (ordinary) chondrites to know there’s a complete absence of evidence for pebble accretion. Chondrites are 100% homogenous until you get down to the little hard things, i.e. there’s zero evidence for their having formed by pebble accretion of marble sized masses forming golf ball sized masses and etc. So the only verifiable statement you can make from chondrites is that pebble accretion works great up to the size of chondrules in the inner solar system!

        Pebble accretion was problematical long before the finding of hot-Jupiters, since the duration of hydrogen in the protoplanetary disk is comparatively brief. As soon as a host star begins to shine, poof!, the most volatile components of hydrogen and helium are outta there.

        Planet migration:

        Planet migration is nothing more than a secondary ad hoc mechanism to prevent the falsification of pebble accretion with the discovery of hot-Jupiters and distant giant planets that couldn’t have been tossed out there by still larger planets closer in, and conveniently, planet migration is non-falsifiable, since the supposed prime mover disappears after the fact. And get this, inward and outward planet migration are EXACT OPPOSITES! How very convenient: mutually contradictory secondary ad hoc mechanisms that are non-falsifiable by definition! (I’ll see to it that this is the poster child for ‘secondary ad hoc tinkering’ under Occam’s razor in Wikipedia after the calliope crashes to the ground.)

        But it gets even better. Having gotten away with the Nice Model, they took it up a notch by layering outward planet migration on top of inward planet migration. Yeah, believe it or not, Jupiter supposedly migrates out after it migrates in, and they still can’t explain hot and cold cubewano populations, the late timing of a late heavy bombardment, the Kuiper cliff, the scattered disc and the doughnut-shaped inner Oort cloud begriming 1000(s) of AU from everything else.

        And looking under the hood, the wheels within wheels are revealed. To sorta, kinda explain the Oort cloud and the late heavy bombardment, we have Neptune progressively evaporating comets inward to Uranus, then Uranus evaporating them in to Saturn and Saturn in to Jupiter before Jupiter catastrophically evaporates them into the Oort cloud!

        So apparently has physics devolved into supercomputer models with sufficient starting conditions and mystery mechanisms to sorta, kinda create the desired result. And everybody bows down and says, “how wonderful”.

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